1. Field of the Invention
The present invention relates to a relief valve for allowing or preventing a fluid flow in a passage and to a method for attaching the same. The present invention also relates to a filter device adopting the relief valve.
2. Related Art
Conventionally, an oil filter device includes a relief valve for allowing oil to bypass a filter element retained in the device when the filter element deteriorates due to some problems such as clogging. This kind of oil filter device is disclosed, for example, in JP-Y2-1-35215, in which the relief valve uses a plurality of openings provided in a cylindrical end plate attached to a lower portion of the filter element.
However, in JP-Y2-1-35215, the relief valve is disposed between the cylindrical end plate and a cylindrical portion of a reinforcing plate with a pushing stress in a radial direction thereof. Further, when the relief valve is elastically deformed to open or close the openings, a deformation stress is applied to the same portion of the relief valve as the pushing stress. Because of this, the relief valve tends to be readily broken. Furthermore, the pushing stress easily varies due to some factors such as a dimension error and an attachment error of the reinforcing plate. The variation in the pushing stress applied to the relief valve adversely affects a valve opening pressure of the relief valve. Therefore, accurate attachment is required, resulting in a low attachment workability.